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    <title>返回文档中的第一个链接的ID</title>
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    <img src="planets.gif" width="145" height="126" alt="Planets" usemap="#planetmap">
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        <area id="sun" shape="rect" coords="0,0,82,126" href="sun.htm" alt="Sun">
        <area id="mercury" shape="circle" coords="90,58,3" href="mercur.htm" alt="Mercury">
        <area id="venus" shape="circle" coords="124,58,8" href="venus.htm" alt="Venus">
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    <p><a id="javascript" href="/js/">JavaScript 教程</a></p>
    <p>第一个链接/地址的ID：
        <script>
            document.write(document.links[0].id);
        </script>
    </p>
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